1. Field of the Invention
Polyoxyalkylene ether polyols, hereinafter for convenience called polyols, are commonly used in the production of urethane polymers. These polyols are reacted with polyisocyanate in the presence of added catalyst and other materials to produce urethane polymers which may be in the form of rubber-like elastomers, flexible or rigid foams and the like. In order that urethane polymers of desired properties and characteristics be produced, it is important that the polyols to be reacted with the polyisocyanate are essentially free of impurities because these impurities may function as undesirable catalysts or otherwise cause undesirable effects in the urethane polymer reaction.
Crude polyols, as commercially prepared, contain various impurities such as alkali metal hydroxide, or other metal salts which were employed as catalysts for the production of polyols. The normal concentrations of catalysts range from 1700 to 4000 parts per million. It is desirable to reduce this to a level of about 5 parts per million or less.
2. Prior Art
One of the commercial practices for the removal of these impurities involves acid neutralization of the alkali forming insoluble salts and removal of same by filtration. Centrifugation, employing mixtures of polyol, water, and solvent can also be employed for the removal of residual catalyst.
The crude polyols without prior neutralization of the catalyst can be treated with a synthetic type adsorbent followed by filtration of the polyol. Another commercial practice involves mixing the polyol and adsorbent with an amount of water ranging from 0.5 to 5.0 percent. Often the polyol quality suffers because of the risk of oxydizing the polyols due to exposure to air during the work-up. This causes the production of off-grade polyol by increasing undesirable acidity.
A number of patents disclose the use of various acidic materials for the neutralization of the alkali metal catalyst followed by filtration of the precipitated salts. Among these are U.S. Pat. Nos. 3,833,669; 3,053,903; 2,983,763; 2,448,664; and 3,016,404. U.S. Pat. No. 3,528,920 discloses the use of synthetic magnesium silicate as an adsorbent for the removal of catalyst from the various glycol ethers. However, this patent also discloses that the undesired alkaline catalyst is first neutralized with an acid prior to filtration. An improvement in efficiency of catalyst removal as described and claimed in U.S. Pat. No. 4,029,879 wherein a critical amount of water is added along with the adsorbent synthetic magnesium silicate prior to heating and filtration. In my copending application, Ser. No. 856,453, an improvement in the process resulting, inter alia, in reduced filtration time is achieved by the addition of carbon dioxide.
None of the prior art references recognizes that an appreciable reduction in the time required for the catalyst removal may be achieved by using a minimal amount of water followed by the addition of magnesium carbonate and then addition of carbon dioxide. In addition, the invention provides for the use of smaller amounts of adsorbent.